1. Field of the Invention
The present invention relates in general to a fin-tube type heat exchanger and, more particularly, to a structural improvement in such a fin-tube type heat exchanger not only for improving heat transfer rate between a fin body and air by forming dimples on the exterior surface of the fin body and but also for facilitating production of the fin-tube type heat exchanger.
2. Description of the Prior Art
With reference to FIGS. 1 to 3, there is shown an example of a typical fin-tube type heat exchanger. In the drawing, the reference numeral 1 denotes a thin plate type fin body. The heat exchanger includes a plurality of fin bodies 1 which are vertically placed in parallel and spaced out at regular intervals. A plurality of tubes 2 laterally penetrate the vertically placed fin bodies 1, so that the tubes 2 are horizontally arranged in the heat exchanger. The tubes 2 are spaced out at regular intervals.
At this time, the tubes 2 are tightly fitted to the fin bodies 1 in such a manner that the opposed ends of the tubes 2 project out of the outside surfaces of the outermost fin bodies 1 respectively. The tubes 2 are tightly fitted to the fin bodies 1 at their contact parts. In order to tightly fit the tubes 2 to the fin bodies 1 at the contact parts, the tubes 2 are fitted into the fin bodies 1 and, thereafter, high pressure air is introduced into the tubes 2 so as to tightly fit the tubes 2 to the fin bodies 2.
As shown in FIGS. 1 to 3, the exterior surface of each fin body 1 is provided with a plurality of louvered fins 3 of a predetermined same shape on their sections free from the tubes 2.
The heat exchanging operation of the above fin-tube type heat exchanger will be described with reference to, for example, an evaporating heat exchanger for an air conditioner.
As well known to those skilled in the art, the temperature of refrigerant flowing in the tubes 2 of the heat exchanger 50 used in the air conditioner is lower than that of the air introduced into the heat exchanger 50. In addition, aluminum typically used as the material of the fin body 1 has an excellent thermal conductivity remarkably higher than that of the air. Therefore, thermal conduction heat transfer is generated in the heat exchanger in order of refrigerant.fwdarw.tubes 2.fwdarw.fin bodies 1 when the refrigerant flows in the tubes 2.
Thereafter, the air introduced into the interior of the heat exchanger 50 comes into contact with not only the exterior surfaces of the fin bodies 1 but also the louvered fins 3 of the fin bodies 1. Therefore, there is a heat transferring action by convection between both the exterior surfaces of the fin bodies 1 and the louvered fins 3 and the air introduced into the heat exchanger 50, thus to let the refrigerant flowing in the tubes 2 evolve or absorb the heat to or from the air.
There have been studied for improving the operational efficiency of heat exchanger by increasing the heat transfer rate by convection between the exterior surfaces of the fin bodies 1 and the air introduced into the heat exchanger 50.
When the air passes by the tubes 2 during its introduction into the heat exchanger 50, separation bubbles are formed about the back surfaces of the tubes 2 due to intrinsic characteristics of air current about the tubes 2 as shown in FIGS. 2 and 4.
At the tube sections having the separation bubbles, the air flow velocity is reduced due to increase of air flow resistance about the tube sections. Therefore, the heat transfer rate of the tube sections having the separation bubbles is lower than that of the other tube sections having no separation bubble.
As described above, the air current characteristics about the tubes 2 exert an important effect upon the heat transfer rate by convection between the exterior surfaces of the fin bodies 1 and the air introduced into the heat exchanger 50.
In an effort to overcome the problem caused by the separation bubbles of the heat exchanger 50 of FIGS. 2 and 3, the louvered fins of the exterior surfaces of the fin bodies 1 may be slitted into thinner louvered fins 4 as shown in FIGS. 4 and 5. In this case, the sizes of the separation bubbles formed about the tubes 2 are reduced, so that it may be possible to improve the heat transfer rate by convection between the exterior surface of the fin bodies 1 and the air introduced into the heat exchanger 50.
However in the above fin-tube type heat exchanger, the thin fin bodies should be provided with the plurality of louvered fins thereon and, furthermore, the louvered fins should be slitted into thinner louvered fins during a louvered fin forming step. In this regard, the above fin-tube type heat exchanger has a problem that a complicated mold should be prepared for production of the heat exchanger. In addition, when the slitted louvered fins have complicated configurations, another problem such as sudden break of the fin bodies may be caused in production of the heat exchanger. A further problem of the above fin-tube type heat exchanger is resided in that the heat exchanger can not effectively reduce the size of the separation bubbles, which bubbles are formed on the back surfaces of the tubes due to air current about the tubes.